U.S. patent number 3,832,054 [Application Number 05/367,487] was granted by the patent office on 1974-08-27 for photographic print timer.
This patent grant is currently assigned to Sable Photo Works, Inc.. Invention is credited to Arthur J. Sable.
United States Patent |
3,832,054 |
Sable |
August 27, 1974 |
PHOTOGRAPHIC PRINT TIMER
Abstract
This invention relates to a multiple-event timer that presents
the user with a limited number of preselected time interval choices
for two or more related events which bear a precise and known
relationship to one another such that the effect of a change in the
time interval for one such event has a predictable effect on its
relationship to the companion events. More particularly, the
instant invention relates to a timer specifically suited for use in
timing the three primary color exposures of a color print being
made by the tri-color printing method wherein the several available
discrete time intervals presented to the user are preselected and
separated from one another by the same equal fraction of a
photographic stop.
Inventors: |
Sable; Arthur J. (Boulder,
CO) |
Assignee: |
Sable Photo Works, Inc.
(Boulder, CO)
|
Family
ID: |
23447370 |
Appl.
No.: |
05/367,487 |
Filed: |
June 6, 1973 |
Current U.S.
Class: |
355/35;
355/36 |
Current CPC
Class: |
G03B
27/73 (20130101) |
Current International
Class: |
G03B
27/73 (20060101); G03b 027/76 () |
Field of
Search: |
;355/35,36,37,38
;356/175,222,223 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Matthews; Samuel S.
Assistant Examiner: Wintercorn; Richard A.
Attorney, Agent or Firm: Edwards, Spangler, Wymore &
Klass
Claims
What is claimed is:
1. The photographic timer which comprises: pulse generating means
operative upon actuation to produce a series of discrete timed
pulses; pulse-counting means connected to the pulse-generating
means operative to receive the timed pulses and repeatedly count
same in cyclic fashion; decoder means connected to the
pulse-counting means adapted to discriminate among the timed pulses
and select therefrom those bearing a logarithmic relationship to
one another amounting to fractional parts of an f-stop; one or more
pulse-selecting means connected to the decoder means, each
operative upon actuation to choose a particular pulse from among
the preselected array thereof; and, triggering means connected to
each pulse selecting means responsive to the particular pulse
chosen by the latter operative to terminate the timing cycle upon
expiration of the chosen time interval.
2. The photographic timer as set forth in claim 1 in which: the
pulse-generating means produces discrete pulses having equal time
intervals therebetween.
3. The photographic timer as set forth in claim 1 in which: the
pulse-generating means cycles approximately once a minute.
4. The photographic timer as set forth in claim 1 in which:
approximately one minute separates the minimum and maximum
preselected time intervals with the minimum being greater than a
second and the maximum being less than 2 minutes.
5. The photographic timer as set forth in claim 1 in which: the
range of preselected time intervals extends from a minimum of
approximately 3 seconds to a maximum of approximately 64
seconds.
6. The timer as set forth in claim 1 in which: at least two
pulse-selecting means are connected to the decoder means and are
independently responsive thereto.
7. The timer as set forth in claim 1 in which: at least two
pulse-selecting means are connected to the decoder means; and, in
which the preselected time intervals available to each of said
pulse-selecting means from the decoder means are chosen such that
incremental changes of the same magitude in two or more of said
selecting means will evoke essentially the same response in the
appropriate emulsion layer of a multi-layer print-making material
irrespective of the overall time intervals to which said selecting
means are set.
8. The timer for timing the component exposures of a color
photographic print which comprises: means connectable to a source
of electrical energy operative upon actuation to repeatedly
generate in cyclic fashion a series of discrete pulses bearing a
logarithmic relationship to one another such that the intervals
therebetween constitute equal fractional parts of an f-stop; means
comprising a selector switch for each color component adjustably
connected to said pulse-generating means adapted upon actuation to
pick a particular pulse during each cycle from the preselected
array thereof independently of the other selector switches; and,
means connected to each of said selector switches responsive to the
particular pulse chosen thereby so as to terminate the component
exposure at the selected time within the cycle.
9. The color print timer as set forth in claim 8 in which: the
pulse-generating means comprises a motor and a notched disk
operatively connected to the motor so as to make a single
revolution in a total elapsed time that exceeds the maximum of the
preselected time intervals, the notches in said disk being spaced
around the rim thereof in a logarithmic fashion corresponding to
the chosen fraction of an f-stop; and, in which said selector
switches each have a plurality of contacts, one of which is
connected to each notch in the disk, and an adjustable switch arm
movable upon actuation to any one contact in the array thereof.
Description
Reasonably precise time control is necessary in the photographic
print making process even when the processor is only making
black-and-white prints although a full f-stop over or underexposure
is difficult for most viewers to detect. In color printing, on the
other hand, accurate time control is essential because even the
average viewer can easily detect a 1/3 f-stop print exposure error
while the trained observer can notice a difference of as little as
one-sixth stop and less.
Unfortunately, precise time control alone, while reasonably easy to
achieve, is far from a complete answer, especially to the timing of
three individual primary color exposures when making a print by the
so-called "tri-color" exposure method. The real problems arise in
connection with introducing the appropriate corrections necessary
to overcome the previously observed condition of improper color
balance. The first problem is knowing how much to increase or
decrease the time interval for a particular color or colors at
different overall exposure times. In other words, just knowing that
the red exposure is too dense by a half stop is not enough when to
decrease the overall red exposure at a 10 second exposure time
means a different thing than to introduce the same correction at a
30 second exposure time. Admittedly, a table can be worked out
rather easily that will tell the user what correction need be made
for a 1/2-stop exposure error at various selected overall time
intervals but to use such a table is time-consuming and most
unhandy.
The correction of a single variable as above noted is simple
compared with the complex problem of correcting for a condition of
color imbalance involving two or all three colors, each of which
has a different overall exposure time. If, for example, the full
color image is too yellow, varying the exposure time of just one of
the three primary colors relative to the other two will not do the
job, but instead, a suitable correction demands that both the red
and green components be cut back to some degree. In the above
instance, while both the red and green would, presumably, have to
be cut back the same amount, this would not manifest itself in the
same time interval corrections due to the fact that the overall
exposure intervals for these two colors will rarely, if ever, be
the same. If we add to this the further complications of having to
correct one primary color more than the other or, perhaps, all
three at once, one can readily appreciate that the problems become
monumental, especially for the amateur photographer who seldom
possesses either the skill or the patience to solve them
correctly.
The prior art photographic timers including the relatively few that
are both sensitive and accurate offer little help for the simple
reason that they offer the user a complete range of time intervals
broken up into seconds or fractions thereof from which he must
select the particular intervals that will produce an acceptable
print. Even if the operator possesses the requisite technical skill
to go back and forth from his interval timer to a correction table
to introduce the appropriate time interval changes necessary to
correct for a condition of color imbalance, to do so is quite
time-consuming and troublesome. It would seem, therefore, that a
prime requisite of a superior photographic timer would be the
elimination of the complete range of possible time interval choices
accompanied by a preselection of a few which would be most useful
while, at the same time, providing all the control necessary to
produce an essentially perfect print.
Next, the increments of time separating these preselected intervals
should, if possible, be chosen such that each means exactly the
same thing in terms of the shift in color balance irrespective of
the duration of the overall exposure time, i.e., whether it be long
or short. In other words, the increase or decrease of the overall
exposure time to the next highest or next lowest preselected time
interval should accomplish precisely the same color shift at an
overall exposure time of 10 seconds as it does at 40 seconds.
Finally, and most important, the preselected exposure times
together with the incremental intervals therebetween for each of
the three primary colors must integrate with those of the other two
such that they will cooperate and enable meaningful and predictable
color shifts to be made where the condition of color imbalance is
the result of a combination of two or all three colors instead of
just one. Saying this another way, it is not only important that an
incremental correction have the same known effect on a given color
regardless of its overall exposure time, it is imperative that the
increments for the timers controlling all three primary color
exposures have the exact same effect on their respective colors so
that a predictable cooperative relationship exists
therebetween.
It has now been found in accordance with the teaching of the
instant invention that these and other worthwhile objectives of a
superior photographic timer can, in fact, be realized by the
simple, yet unobvious, expedient of preselecting a series of time
intervals for the three primary colors that bear a logarithmic
relationship to one another and in which the intervals therebetween
correspond to the same fractional divisions of an f-stop in all
three scales as well as each scale individually.
It is, therefore, the principle object of the present invention to
provide a novel and improved multiple-event timer.
A second objective of the within-described invention is the
provision of a timer of the class described which is ideally suited
and especially adapted for use in timing the primary color
exposures of a color print being made by the tri-color printing
process.
Another object is to provide a photographic print timer in which
the available time intervals are preselected.
Still another objective is the provision of a timer for
photographic prints wherein the preselected exposure times bear a
logarithmic relationship to one another.
An additional object is to provide a timer for color print-making
of the type disclosed and claimed herein in which the same
intervals separate the preselected times in all three time scales
as well as in each scale individually and in which such interval
corresponds to a fractional part of an f-stop.
Other objects will be in part apparent and in part pointed out
specifically hereinafter in connection with the description of the
drawings that follows, and in which:
FIG. 1 is a schematic view showing an electro-mechanical embodiment
of the timer employing a notched disk as the means for activating
the multi-contact selector switch at preselected time
intervals;
FIG. 2 is a schematic view showing a second electro-mechanical
embodiment in which the timing motor actuates a reed switch, the
pulses of which are fed to a stepper;
FIG. 3 is a block diagram illustrating a timing circuit utilizing a
pulse generator, a pulse counter to count the timed pulses from the
generator and a decoder to deliver a preselected array of pulses to
the selectors;
FIG. 4 is a block diagram similar to FIG. 3 but showing a
synchronous motor and reed switch used as the pulse generator, a
pair of steppers as the pulse counter and selector switches
connected to the latter in a manner to preselect certain pulses
from the array thereof;
FIG. 5 is a schematic diagram of the timing circuit shown in the
block diagram of FIG. 4;
FIG. 6 is a schematic view showing the manner in which all of the
selector switches are connected to the steppers in a manner to
select timed intervals therefrom bearing the logarithmic
relationship to one another predicated upon fractions of an
f-stop;
FIG. 7 is a block diagram illustrating an electronic timing circuit
of the general type exemplified in FIG. 3;
FIG. 8 is a schematic diagram of the electronic timing circuit of
FIG. 7; and,
FIG. 9 is a wiring diagram showing how each of the 12-position
4-pole selector switches are connected to the output of the
cascaded binary counters so as to provide a preselected set of
exposure times bearing a logarithmic relationship to one another
with the intervals therebetween comprising equal fractions of an
f-stop.
Referring next to the drawings for a detailed explanation of the
present invention and, initially, to FIG. 1 for this purpose,
probably one of the simplest forms of the timer comprises an
electric motor 10 of a type adapted to make one complete revolution
in a total time interval that slightly exceeds the longest time
interval of the preselected choices. Thus, if we select a time
scale covering a total of 60 seconds, then the motor should make
one complete revolution in something in excess of 1 minute, say 65
seconds. In accordance with the teaching found herein, instead of
dividing the foregoing maximum time interval up into a full
complement of possible choices broken down to tenths of a second as
is commonly done in the prior art photographic timers, a series of
preselected increments will be chosen that are arrayed in a
logarithmic relationship to one another that corresponds to
fractions of an f-stop. For instance, if we choose increments of
one-third stop, the preselected discrete time intervals would be as
follows starting at, say a minimum interval of 3 seconds: 3.0 3.75
4.75 6.0 7.5 9.5 12.0 15.0 19.0 24.0 30.0 38,0 48.0 60.0
Now, as represented schematically in FIG. 1, a single
peripherally-notched disk 12 would be driven in synchronous fashion
by the motor 10 so as to complete one full revolution in 65
seconds. A total of 15 notches, 1 through 15, would be provided in
the periphery of the disk if the above logarithmic scale is used
including as the first notch, the one corresponding to zero time.
Instead of the notches being equiangulary-spaced around the
circumference of disk 12, they are, of course, located relative to
the first notch in accordance with the particular time interval
they represent. In the schematic of FIG. 1, each notch is shown
linked mechanically to a companion switch denominated S.phi., S3.0
. . . S48, S60 in accordance with the time scale. In the particular
form illustrated, switches S.phi. - S60 are of the single pole
double-throw type which function upon arrival of the disk at the
notch to which they are mechanically linked to momentarily shift to
the open contact of the pair.
In operation, closure of the normally-open start switch 14 latches
in relay 16 to turn on the timing motor 10. After enough time has
elapsed for the motor to reach synchronous speed, the disk 12
driven thereby reaches notch 1 and actuates the companion switch
S.phi. linked thereto in a manner to momentarily energize relay 18
which latches itself in. The latter relay turns on the enlarger
lamp 20 at time zero.
Presumably, the operator has already determined a set of exposure
times for the red, green and blue components of the finished color
print from among those preselected choices made available to him.
In accordance with such selections, the operator will set each of
the three selector switches R22, B22 and G22 on the contact thereof
connected to the switch (S1-S60) corresponding to the particular
time interval chosen.
When switches B22 and G22 are actuated through the chosen contact
by the S-switch connected in series therewith, they each energize a
solenoid G24 and B24 in the particular embodiment illustrated.
These solenoids might be used by way of example to move magenta and
yellow subtractive filters into the light path in accordance with
the teaching of my copending application Ser. No. 223,081, now U.S.
Patent No. 3,797,933, issued Mar. 19, 1974, to terminate the green
and blue exposures, respectively. This particular circuit is
predicated upon the assumption that the red exposure will be the
longest of the three, therefore, when red selector switch R22
actuates, it will deenergize relay 18 thus extinguishing the
enlarger lamp and terminating the red exposure as red light is the
only color that is still being allowed to pass through the
subtractive filters.
The final step in the cycle is to trip switch S60 which reopens
relay 16 and stops the motor 10. As it does so, the motor 10 and
disk 12 will coast far enough to pass notch 15 in the latter and
reset the switch S60 so that it will, once again, operate to latch
relay 16 upon closure of the start switch. This feature also allows
the motor to get up to synchronous speed before notch 1 is reached
on the disk that actuates switch S.phi. and turns on lamp 20.
As an alternative to the above, the motor could carry three
identical disks 12, each connected to its own set of switches. Such
a construction would, of course, be more expensive and no
significant advantage would be gained over the single-disk
embodiment illustrated.
Next, with reference to the circuit diagram of FIG. 2, a second
slightly different form of timer has been illustrated wherein the
synchronous motor 10 carries a cam (shown schematically by broken
line 12M) that is analogous to the notched disk of the FIG. 1
embodiment in that its peripheral margin is formed to actuate a
single switch 28 repeatedly at each of the preselected time
intervals as well as at the start of the timing cycle. A stepping
switch 30 connected to the cam-actuated switch 28 responds to each
closure of the latter and counts them in the usual way by stepping
from contact to contact thereof.
In the specific circuit shown in FIG. 2, closure of the normally
open start switch 14 pulls in relay 32 and latches it in closed
position. Relay 32 along with the other relays in the circuit which
will be described shortly are all of the conventional two-winding
latch-unlatch type, either magnetic or mechanical. When relay 32
latches in, the timing motor 10 is energized and power is supplied
to the stepper circuit. After a brief time during which the motor
comes up to speed, the cam 12M carried thereby will make the
initial closure of cam-actuated switch 28 which, in turn, advances
the stepper onto its zero contact. With the zero contact thus
energized momentarily, relay 34 latches in turning on the enlarger
lamp 20 as before.
The red, green and blue selector switches R22, G22 and B22 are set
as in the previously-described circuit on the contact thereof that
represents the particular preselected time interval the operator
has chosen to expose each primary color in the finished print. As
before in the case of the green and blue selector switches G22 and
B22, when the stepper has been advanced by the cam-operated switch
28 to the live contacts, the solenoids G24 and B24 controlled
thereby will be energized to move appropriate subtractive
filtration into place assuming the timer is being used to make
prints by the subtractive tri-color method for which my enlarger is
designed. Obviously, both the timer circuits of FIGS. 1 and 2 could
readily be adapted to other color printing methods without the
exercise of invention and the ones shown are intended as being
merely representative of the type of circuit that can be controlled
by the digital timer of the present invention.
Once again, we will operate upon the assumption that the red
exposure is the longest of the three so that when the stepper
advances to its live contact, the "unlatch" coil of relay 34 will
be energized to drop it out and turn off the enlarger lamp. It is
to be understood, of course, that stepper 30 will have at least
fifteen stepped contacts to accommodate the 14 preselected
intervals and one at the start or time zero. The intervals at which
the stepper advances will be determined by the cam 12M actuating
switch 28.
Once the stepper has advanced all the way to the last contact in
the series (contact 14 if we assume the same set of preselected
intervals set forth earlier), it will drop out relay 32 by
energizing the unlatch coil thereof. With power no longer supplied
to motor 10, it will coast to a point where the cam 12M leaves the
cam-actuated switch 28 open prepared to begin another cycle. The
start switch 14 has, of course, reopened and when it closes to
relatch relay 32 and start the motor, the latter will be able to
get up to speed before the cam-actuated switch closes to advance
the stepper onto its zero contact.
The remaining two specific embodiments differ from those just
described in that instead of generating a series of discrete pulses
that already bear a preselected logarithmic relationship, a pulse
generator is used that generates a series of pulses equally-spaced
in time. These pulses are then counted by a divider or counter
which has a unique combination of output signals for each count
within its range. The counter outputs are decoded and certain
preselected counts are chosen from among the available array
thereof corresponding to the particular exposure times the operator
will need to the exclusion of all others. From this preselected
array, the operator then chooses one for each color component of
the final print and it is used to initiate an operation such as the
one already described, namely, the termination of a
previously-initiated exposure.
A block diagram of such a timer has been illustrated in FIG. 3
where reference numeral 36 designates the pulse generator keyed to
the 60Hz power line frequency. The equally-spaced pulses generated
by the latter are fed to a pulse counter 38 where a decoder 40
picks certain pulses therefrom that bear a logarithmic relationship
to one another corresponding to fractional portions of an f-stop.
Two or more selectors 42R, 42G and 42B are connected in parallel
with one another to receive the predetermined output of the decoder
from which the operator makes a single selection.
FIGS. 4, 5 and 6 to which reference will now be made are directed
to a specific electro-mechanical embodiment of the timer
represented by the block diagram of FIG. 3. The pulse generator
indicated in a general way by numeral 36 comprises a synchronous
motor 44 and a magnetic reed switch 46. The motor is driven at a
constant accurate speed from the 60Hz power source and its output
shaft (represented schematically in FIG. 5 by broken line 48) is
geared down to turn at a relatively slow speed such as, for
example, 120 r.p.m. A magnet (not shown) attached to this output
shaft rotates at this frequency in operative proximity to the
magnetic reed switch 46 which responds by opening and closing each
time the magnet turns end-for-end so that two pulses per revolution
of four pulses per second are generated in equally-spaced relation
with reference to time. The pulses thus generated are fed to a pair
of cascaded 12-position electro-mechanical stepping switches 50 and
52 connected such that switch 50 increments one position with each
pulse and repeats after the 12th pulse, whereas, switch 52
increments one position after the first one completes each cycle,
i.e., every 12th pulse. Thus, the first stepper 50 completes a
cycle every 3 seconds and the second stepper 52 every 36 seconds.
As thus designed, one has a choice of time intervals up to a
maximum of 36 seconds broken down into 1/4 second equal increments
since there is a unique combination of stepper positions for each
of the 144 increments.
It is from this point on that the timer becomes unique among
photographic timers because, instead of providing the user with a
full range of discrete time intervals, the steps of which are
equally spaced with reference to time and have no particular
significance as far as print density is concerned, the instant
apparatus preselects from the foregoing array of time intervals
only those that bear a known and useful relationship to the
photographic print-making process, namely, those that will yield
equal changes in print density. More specifically, only those
discrete time intervals are selected and made available to the user
which bear a constant logarithmic relationship to one another
predicated upon fractions of an f-stop. It is only when this is
done that the operator knows that increasing or decreasing the
overall time interval by a one or more increment within the
reciprocity limits of the print making material will have
substantially the same effect on print density regardless of the
particular overall exposure interval. In addition, he knows that
each incremental change to shorten or lengthen the overall exposure
times of two or all three primary colors will result in the
selfsame change in the density of the color in the emulsion layer
of the print making material responsive thereto even though the
overall time intervals themselves are entirely different.
Furthermore, and most significant, the user is, for the first time,
provided with the means by which a condition of color imbalance
brought about by a mixture of two or even all three primary colors
can easily and predictably be changed into its proper relationship
by making incremental shifts in the colors effected which bear a
known cooperative relationship to one another that is substantially
independent of their respective overall exposure times.
Accordingly, the stepper positions corresponding to the preselected
time intervals chosen as above-noted from which the user can choose
are wired to selector switches 42G, 42B and 42R in accordance with
the wiring diagram of FIG. 6 showing one such switch, the other two
being wired identically to the one shown. The switch arms 54 and 56
(FIG. 5) of these selector switches are live only when the
preselected pulse count is reached. These switch arms are in turn
connected to actuate the timed operation to be performed such as,
for example, to energize relays G24 and B24 to insert the
subtractive filters in the light to become operative to terminate
the green and blue component exposures and to deactuate the relay
58 that is keeping the enlarger lamp 20 lit.
Specifically with reference to FIG. 5, switch 60 is of the
single-pole double-throw type operative in one position to energize
the enlarger lamp 20 independently of the timer circuit for
focusing purposes and in its second position to actuate the timer
circuit. Switch 62 is a momentary contact switch employed to
initiate the timing cycle. Closure of the latter causes relay 64 to
pull in and latch through its own contacts thus starting motor 44
that actuates reed switch 46 twice each revolution. Relay 64 as
well as relays 58, 66, 68 and 70 are all of the double-pole
double-throw type even though not all the contacts are used.
In operation, since the motor takes a little time to reach
synchronous speed, it is turned on a few pulses in advance of zero
time on the steppers 50 and 52, both of which are 12-position
single-pole stepping switches of conventional design. The pulses
occurring each one-fourth second from reed swtich 46 advance
stepper 50 through its 12 pulses, whereupon, stepper 52 advances
one step with each 12th pulse of stepper 50. When the 0-0 position
(zero on both steppers) is reached, relay 66 is pulled in
momentarily and it, in turn, pulls in relay 68 which latches in
through its own contacts and turns on the enlarger lamp 20.
If, for example, contact 4 on stepper 50 and contact 6 on stepper
52 were connected to the "N" contact of selector 42G, this would
mean that the latter contact would be live after a time lapse of
19.0 seconds which is one of our preselected time intervals.
Stepper 52 will have advanced six increments corresponding to 18
seconds (stepper 50 steps a full cycle every three seconds) and
four steps on stepper 50 amounting to one additional second. Then,
if as assumed previously, we have preselected time intervals in 1/3
f-stop increments starting with 3.75 seconds as shown in FIG. 6,
the ninth or "H-S" pair of contacts will correspond to 19.0
seconds. If the green component time interval is b 19.0 seconds as
set on selector 42G, then the green solenoid G24 will energize
momentarily to actuate and initiate the termination of the green
component exposure, probably by interposing a magenta filter in the
light path. A similar sequence is followed to actuate blue solenoid
B24 at the preselected time interval for the blue component
exposure to move a yellow filter in place or otherwise terminate
the blue exposure. When, however, the steppers 50 and 52 step to
the time interval set on selector switch 42R, relay 58 is
momentarily pulled in which unlatches relay 68 causing it to drop
out and extinguish the enlarger lamp. The steppers, however,
continue to advance incrementally until they reach position 5-11,
whereupon, relay 70 is momentarily pulled in thus unlatching relay
64 causing it to drop out and turn off the motor while deenergizing
the steppers 50 and 52. These steppers, therefore, come to rest a
few positions before position 0--0 giving the motor time to get up
to synchronous speed before the timing cycle is initiated.
Next, with reference to the remaining figures of the drawings,
specifically, FIGS. 7, 8 and 9, the fourth and final version of the
timer, a fully electronic one, will be described in detail. In the
latter, both the generation of the pulses and the counting thereof
is done electronically instead of electro-mechanically as was the
case in the version just described.
The pulse generator 36m shown in the block diagram of FIG. 7
comprises a voltage comparator which generates a pulse with each
positive zerocrossing of the 60Hz power line voltage which, of
course, occurs every 1/60th of a second. The pulses thus generated
are then fed to a divide-by-15 counter 38m that reduces the pulse
count to 4 per second. The 1/4-second pulses then go to an 8-bit
binary counter 40m consisting of eight cascaded flip-flops. From
this arrangement results 256 unique combinations of flip-flop
outputs thereby providing a selection of possible time intervals up
to 64 seconds in 1/4-second increments. For each position, these
selected lines are ANDed together, and the output thus joined is
used to actuate the desired operation at the selected time for each
selector switch 42Gm, 42Bm and 42Rm as will appear presently.
In the schematic diagram of FIG. 8 to which detailed reference will
now be made, the commercially-available voltage comparator 36m is a
conventional integrated circuit voltage comparator such as industry
type LM 311. Divide-by-15 counter 38m comprises three 4-bit binary
counter integrated circuits 72a, 72b and 72c such as, for example,
type SN 7493. Reference numeral 74 has been chosen to designate a
5-volt integrated circuit voltage regulator such as type SN 75451.
The selector switches 42Gm, 42Bm and 42Rm are 12-position 4-pole
selector switches, preferably of the conventional
multiple-pushbutton interlocking type. Interposed between these
selector switches and the green and blue solenoids G24 and B24 are
integrated-circuit dual high-current drivers 76 and 78 such as type
SN 75451, both of which have been shown in FIG. 7. Reference
numeral 80, on the other hand, identifies a quad 2-input NAND gate
integrated circuit such as type SN 7400, whereas, 82 and 84 are
dual 4-input NAND gate integrated circuits such as type SN 7420.
Relay 86 is one having a 12-volt coil and single-pole single-throw
normally open contacts.
With these specifics concerning the circuit in mind, it will be
apparent that a momentary closure of start switch 62 will cause the
flip-flop comprising gates 80(1) and 80(2) of NAND gate 80 to
change state. This causes relay driver 76 to turn on pulling in
relay 86 thereby turning on enlarger lamp 20. This same change in
state of the flip-flop also results in the reset-inhibit inputs of
the counters 72a, 72b and 72c going low thus permitting them to
begin counting the pulses generated by comparator 36m from the 60Hz
line. The counter string consists of a divide-by-15 counter 38m
comprised of counter 72a together with feedback gates including
half 82(1) of NAND gate 82 and one-quarter 80(3) of NAND gate 80
followed by an 8-bit binary counter comprising 4-bit counters 72b
and 72c cascaded.
When the binary counter string 40m reaches the count corresponding
to the particular choice of preselected intervals available on
selector switch 42Gm, the four inputs of the NAND gate 82(2)
comprising the remaining half of gate 82 all go to high
simultaneously causing driver 78(1) which is half of NAND gate 78
to turn on momentarily thus actuating the green solenoid G24 to
terminate the green exposure by interposing a magenta filter in the
light path as before.
Similarly, when the binary counter string 40m reaches the count
corresponding to the chosen time interval from among the
preselected ones available on selector switch 42Bm, the four inputs
to the NAND gate 84(1) that comprises half of NAND gate 84 all go
high simultaneously causing driver 78(2) which is the remaining
half of NAND gate 78 to turn on momentarily thereby actuating the
blue solenoid B24 to terminate the blue component exposure such as
by interposing a yellow filter in the light path.
Finally, when the binary counter string reaches the count
corresponding to the time interval chosen from among the
preselected times available on selector switch 42Rm, the four
inputs to the other half 84(2) of NAND gate 84 all go high at the
same instant causing flip-flop 80 to revert back to its original
state. This results in driver 76 turning off to drop out relay 86
and extinguishing the enlarger lamp 20 to terminate the red
exposure, the blue and green exposures having been terminated
previously. When flip-flop 80 changes state as above mentioned, the
reset-inhibit inputs of the counters go high thus resetting them to
zero and holding them there. The timer is thus readied for another
cycle.
In conclusion, FIG. 9 shows one of the three selector switches 42
together with its four-input NAND gate. All three of the selector
switches 42Gm, 42Bm and 42Rm are wired identically although the
output of the latter is used to extinguish the enlarger lamp 20
while that of the first two is employed to bring a subtractive
filter into the light beam. Actually, of course, while we have
assumed that the red component is the longest of the three
exposures for convenience sake, this needn't be true and either of
the other two could have been used. Likewise, while the timer has
been described as it would be used to make a print by the tricolor
subtractive technique, it should be perfectly obvious that it is
equally adaptable to other color printing techniques as well as
black-and-white.
FIG. 9 reveals the manner in which the selector switches 42 would
be wired to take the four pulses per second from the cascaded
binary counters and make available to the user the preselected
pattern of time intervals predicated upon fractional f-stop
increments beginning with 3.75 seconds and going all the way up to
48 seconds where every third increment is doubled.
In the foregoing description, the various timer embodiments have
been designed around a set of preselected time intervals bearing
equal fractional increments amounting to either 1/3 or 1/4f-stops
to one another, however, it is apparent that other fractional
increments can be used without the exercise of invention. It is
also significant that the total range of preselected times be
chosen such that no serious reciprocity failure occur in the print
making material. In other words, by preselecting a range of times
for the operator that are no shorter than 3 seconds or so and no
longer than approximately 60 seconds, then the preselected equal
fractional increments produce essentially the same response in any
of the emulsion layers of the print making material at the minimum
as well as the maximum available exposure times. While it is
undoubtedly possible to compensate for the known variations in
response of the emulsion layers of the print making material by
lengthening the already unequal intervals for the long exposure
times while foreshortening those that are quite short, by far the
simplest and more practical approach is to limit the range of
preselected choices to that wherein the equal fractional f-stop
increments remain valid and evoke essentially the same response in
the emulsion.
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